Optical projection systems



April 10, 1956 R. E. REAsoN ETAL 2,741,153

OPTICAL PROJECTION SYSTEMS Filed Sept. l5, 1952 4 Sheets-Sheet l f L 1l April 1o, 1956 Filed Sept. l5,l 1952 OPTICAL PROJECTION SYSTEMS 4 Sheets-Sheet 2 Inventor By M GWA! 1 68cm Attorney April 10, 1956 R. E. REASON ET AL OPTICAL PROJECTION SYSTEMS 4 Sheets-Sheet 3 Filed sept. 15. 1952 IFI/9.8. M/KB E@ F/G/O. M2

Inventor A ttorney April 10, 1956 Filed Sept. l5, 1952 lR. E. REASON ET AL OPTICAL PROJECTION SYSTEMS 4 Sheets-Sheet 4 Irl' F/G/S.

Inventor 'mhb E- Rin so N 5m-xu R' Gum-HS Hartman R. Cdemqni nited States Patent OP'HCAL PPHECTQN 'SYST EMS Richarl Edmund Reason, John Reginald Adams, and Kenneth Roy Coleman, Leicester, England, assignors to Kapelle: Limited, Leicester, England, a British com- Dany Application September 15, I1952, Serial No. 369,666

Claims priority, Yappliczation Great Britain Septemberl, 1951 12 Claims. (Cl. 88-24) This invention relates to optical projection systems, primarily intended for use'in optical apparatus for measuring or testing the accuracy of plane section proiiles. In one known arrangement of such apparatus, an illuminating device is employed to produce on the surface of a body to be examined a line of light which defines the plane section profile thereon, and an optical projection system is provided to form -an image of such illuminated section profile in an image plane, for example on a projection screen, where it can be accurately measured or compared with a standard profile.

This invention, although not limitedthereto, is more especially intended for use in apparatus for the examination of bodies, such as turbine blades, for which it is desirable to measure or test not only the shapes and sizes of individual plane section proiiles but also the positions of such proles relatively to one another.

The present invention is concerned with an optical system for simultaneously projecting on -to a single image plane images of the profiles of two or more plane sections of a body in planes parallel to but at dierent distances from suchimage plane, and the system according tothe invention comprises one or more plane reflectors associated with individual section profiles and so'located as to bring reected images thereof all into a single object plane, and an objective for projecting an image from such object plane on to the image plane. The object plane may corxveniently coincide with the plane of the section prole furthest from the objective, the number of plane reiiectors being one less than the number of section profiles.

The plane reectors may be (totally reflecting and so shaped as to act as partial screens forfsegregating zones of the objective for association with individual section profiles. Such zones may be annular, 'the inner edge of each reector being spaced away lfrom the body to be examined, so that rays from the section proiile associated with the reflector pass'to an annular zone of the Vobjective whilst rays from another section -prole pass through the space between the reectorand the body to an inner zone of the objective. Alternately, the vzones may be generally sector-shaped, each reflector being formed of a number of angularly spaced elements approximately of sector shape.

In another arrangement, the plane reiiectors are partially transparent over their whole field, and in such case the transmittance of the partially transparent reectors is preferably graded from reector to reiiector so that the intensity of the beam of light passing through the objec'tive vfrom any one section profile is substantially the same as that for any other section profile. In order to obtain adequate brightness of the image, and also to make it possible to project an image of the complete section proles around the whole periphery of the body, it will usually be desirable for each reector to have a central opening shaped to conform closely to the'peripheral'shape of the body at the position .atwhich'the reflector is to be mounted.

When Ythe bodiesto `be, examined are ofrelatively com- `ing drawings.

'the same time. to examine one face onlyofithe blade, it will moreusually vround 4the whole perimeter of 'the blade.

ICC

plex shape, as for example in the case of turbine blades, diticulty `may be experienced in vloading the Vbodies into position in the reilector assembly without fouling the reilectors. For it will usually be desirable to coat the surface of the body with amatt iilrnto increase the llight intensity of the rays used for projecting the image, and it is therefore especially'important to avoid any rubbing of -the body surface against the edges of thelopenings in the reectors. In some instances the shape of the body maybe such that this ditculty can be overcome by accurately guiding the loading movement ofthe body, Vand thiskwill usually suffice when using totally reecting Vreiiectors `arranged for annular zone segregation.

In the case of radial lzone segregation, the diiiiculty -can be met by so mounting the sector-shaped elements of each reflector that they can be moved in a plane at right angles to the optical axis of the-objective towards and away from such axis. Thus the elements may be mounted to slide in approximately radial guides under the control ofvcams carried by a rotatable ring.

In the case of partially transparent reectors, it will usually be desirable to form each reector in two or more parts which can be moved towards or away from each other in a plane at right -angles to the optical axis of the objective, in order to provide the requisite clearances for the loading movement. In Vone -convenient arrangement for this purpose, the mounting 'for each reilector comprises a plane guide surface lying accurately at right angles to the optical axis of the objective, and movable frames which can slide over such guide surface and are springpressed into engagement therewith, the reiiector parts being so mounted respectively in the frames that their reiiecting surfaces lie accurately parallel to Vthe plane of engagement of the frames with the guide surface.

VIn practice it will usually be desirable for the apparatus to be such that bodies of dierent sizes and shapes can be examined. This can -often be satisfactorily achieved by providing a diterent reflectorassernbly for -each different size and shape of bodywith which the apparatus is required to deal. Alternatively, means may be provided whereby the positions of 'the reflectors :can be adjusted in the direction of the optical axis of `the `objective to suit diterent spacings between the planes ofthe section protiles. In such case, whenthe reectors have central openings conforming'to the contour'of the body, the reiiector mountings may be axially adjustable, eachfreilector being .detachably iitted in its mounting, so that it can -be removed when the mounting is adjusted and replaced by another reflector vWhose central opening conforms to the peripheral'shape of the body in theadjusted position.

The invention may be carried into practice in various ways, but some convenient alternative practical examples according thereto are illustrated in the accompany- These examples are shown, for convenience, as applied to their use -fortesting the accuracy of manufacture of turbine blades of-aerofoil section, wherein be suicient in practice to 'examine simultaneously the `prot-iles of two sections respectively near the two ends of the blade, whilst for a more thorough test a third section near the middle Vof the blade may 'also be examined at Whilst in some instances Ait may Vsutil-ice be important to examine the complete -section profiles The arrangements illustrated make `,this possible, y.and .are also such that they can readily be adjusted .to dealwithdieren't sizes of blade, for which -of course diierent :spacing between .the section planes 'will be required. in the drawings,

Figure l shows a generalview of'one convenient con- Patented Apr. 10, 1956.

struction of the apparatus according to the invention, to

Vwhich the alternative reector arrangements illustrated in the remaining figures can be applied, parts being shown in section to show their arrangement more clearly,

Figures 2 and 3 show, respectively in section and in face view, the relector arrangement indicated in Figure l,

Figure 4 is a diagrammatic view of part of an alternative arrangement employing a partially transparent re- Hector,

Figures 10, 1l and l2 are sections respectively on the lines X-X and Xl-Xl of Figure 8 and XII-XH of Figure 9, and

Figures l3-l5 illustrate a further alternative arrangement employing a divided fully reflecting reflector, Figure l3 showing the reilector and its mounting in face view, whilst Figures 14 and l5 are sectional views respectively on the lines XlV-XlV and XV-V of Figure 13.V

ln the apparatus shown in Figure l, the turbine blade A to be examined is detachably mounted by its root Al in a chuck or other holder B movably mounted on the xed base C or" the apparatus, the arrangement being such that, when the holder B has been properly positioned, the chosen plane section A2 nearest the root of the blade A will always occupy the same plane relatively to the fixed base C, whatever the size and shape or the blade.

The fixed-base VC also carries an illuminating device for defining theV section protiles on the surface of the blade A, the example illustrated being arranged to provide two section profiles, one A2 in the xed plane above mentioned and the other A3 towards the tip of the blade. The illuminating device (which in itself forms no part of the present invention) may be arranged in various ways, but in the example illustrated comprises four similar illuminators DD1D2D3, two of which DB1 serve to define the section profile A2 from opposite sides of the blade, whilst the other two DZD3 similarly dene the section protile A3. The four illuminators DD1D`2D3 are respectively carried on four arms EE1E2E3 mounted to slide in suitable guides carried by the ixed base C, the arms being held against rotation either by their crosssectional shape or by suitable keying. In practice, the arms EE1E2E3 are adjusted in their slides to suit the par- Vtcular blade A being tested, distance pieces E4E5E5E7 being used for accurate setting, the arms when correctly adjusted being clamped in position. Each illuminator comprises a source of light D4 with a suitable condensing `lens D5, a mask D6 in the form of a slit or knife edge shaded to suit the section profile, and a lens D'1 for focussing an image of the mask D6 on the surface of the blade A. 1n order to increase Vthe light intensity of the rays used for projecting the images of the section protiles thus deined, it will usually be desirable to coat the blade surface with a matt white film, such for example as a film of magnesium oxide.

The present invention is concerned with the ,simulltaneous projection of images of the two or more section profiles onto a single image plane, where such images can be measured or compared vwith standard profiles.

lt has already been mentioned that the section plane A2 Y nearest the root of the blade A always occupies the same described in detail below) to image the other section profile A3 or profiles on to this same object'plane A2, and it will be at once clear that this enables a projecting objective F simultaneously to focus images of all the section proiles accurately' on a single image plane. The obective F may be arranged to produce enlarged images of the section profiles AZA3 on a projection screen F1, which may if desired bear markings of standard Vblade section proles for comparison purposes, or alternatively may produce a small image iu the image plane for viewtlirough a microscope, which may be provided with a graticule bearing the standard markings.

The various alternative arrangements according to the invention diler from one another in respect of the arrangement of the reflectors. In all cases, since the section profile A2 nearest the root of the blade A is directly projected without the use of a retiector, the number of relie/:tors used will be one less than the number of section profiles, so that if two section profiles only are to e projected, as shown, only one reilector will be needed, Whilst if there are three section profiles, two reectors will be used, each reflector being mounted with its reilecting surface in a plane half-way between the plane of the section proile and the common object plane, due allowance being made where necessary for the thickness of any glass through which the rays have to pass. The reector, or each reector, is carried on a bracket C1 mounted to slide on a slideway C2 on the xed base C, to enable it to be adjusted to the correct position, a distance piece C3 preferably being used for accurate setting.

ln the example indicated in Figure l and shown on a larger scale in Figures 2 and 3, the rellector (or each partial reflector if made in separable parts) consists ot an orfully reflecting mirror G with front surface reilection. trated, with the section profile A3 near the tip of the blade and acts as a screen to cut oli part of the beam from the other section prole A2, so that the section proiles are associated with annular zones of the proiection obiective l?. v Although it would "ce possible for the reflector G to lit closely round the blade A and to have relatively limit-sd external radial dimensions, so that the innermost :one would be occupied by the rays trom the section profile A3 nearest the tip of the blade and the outermost zone by the rays from the section prolile A2 nearest the root of the blade, it will usually be more convenient, as shown, to adopt the reverse arrangement, the inner edge of the rellector G being spaced away from the blade to permit the passage of the rays from the section prole A2 to the innermost zone of the objective, the rays from the profile A3 being confined to the outermost zone. This latter arrangement has the advantage that the central opening in the reiiector will usually be large enough to facilitate loading of the blade into position without fouling the reiiector, especially if (as shown in Figure l) the blade holder B is provided with a helical groove Bl coacting with a xed pin B2, so that the blade will twist somewhat in its axial movement into or out of the opera- Vtive position to an extent suited to the shape of the blade.

The size and shape of the central opening in the reliector G (or of each reector, it there is more than one) are so chosen as to give approximately equal light intensities for the images of the individual section proles. f Some degree of latitude is permissible in this respect, however, so that it will often be practicable to cater for diii'erent sizes of blade by axial adjustment of the reflector (as shown in Figure l) without need for substitution of another reflector having a central opening of diilerent size or shape.

instead of using a fully retlecting mirror as the redector it will often be preferable to employ a partially transparent retlector, consisting for example of a plate of glass Y partially metallised over the whole area of one surface, so that part of the light incident on the partially reecting surface is transmitted through the surface and part is reflected. Such an arrangement is shown in Figure 4 for This reilector G is associated, in the example illus--V the case oi one reliector H, whilst Figure shows a similar arrangement with two redectors H11-l2 for dealing with three section proles, the third section profile A4 being somewhat displaced from halfway between the section profiles A2 and A3 so as to be clear of the reflector H. The reflector H, or each retiector H1 or H2, is located with its metallised surface slightly displaced from the haifway position between the fixed section profile A2 and its associated section profile A3 or A4 to allow for the slight difference in ray paths due to the thickness of the glass.

lt is desirable to grade the transinittance of the redectors, in order to obtain substantially the same light intensity in the images of the individual section profiles. Thus in the arrangement of Figure 4, the one reector H should have 50 per cent transmittance, so that the intensities of the two emergent beams from the two section profiles A2A3 should be equal to one another. In the arrangement ot' Figure 5, the reflector H2 nearest to the object plane of the objective F should have 50 per cent transmittance, so that the emergent beams respectively from the section profiles A2 and A4 will have equal intensities. The other reector Hl however should have 662/3 per cent transmittance, so that the intensities of the beams from the first two section proles A2A4, already reduced to half at the rst reflector H2, will be reduced to onethird of their original values on transmission through the second reliector H1, whilst the intensity of the beam from the third section prole A3 will likewise be reduced to one-third on reilection at the second reector H1. lf there were a third reiector, its transmittance should be 75 per cent, the intensity of each beam being reduced to a quarter of its original value, and so on.

Figure 6 shows a preferred practical form of partially transparent reiiector comprising two glass plates Hill-i4 in contact with one another, having one of the two contacting surfaces provided with the metallised coating. This arrangement, not only alords protection against damage to the metallised coating, but also has the advantage of equalising the transmitted and reected ray paths, so that the'metallised surface should be located exactly halfway between its associated section prolile and the object plane of the objective F.

It is important that each reflector (or H1 or H2 or H2H4) should surround the blade A with as little clear ance as is practicable, as indicated in Figure 7. This, however, will often give rise to practical diiiiculty in loading the blade into position within the reliector assembly, owing to the twist of the blade, for it is important that during loading the blade should not rub against the edge of the central hole in the reiiector.

lt wl be appreciated, therefore, that it is only with certain shapes of turbine blade, wherein the twist is suitable, that it is practicable to malte the reflectorin one piece. in such case it is important to provide a generally helical guide track B1, suited to the twist of the blade A, so that as the blade holder B is moved axially into its operative position it will automatically turn on its axis to the correct degree to ensure that the blade will pass through the central opening in the reflector H (or in each reflector it more than one is provided) without touching the edge thereof.

Generally, however, it is preferable to divide the reector (or each reflector) into two parts movable towards or away from one another in a plane at right angles to the optical axis of the projecting system. lt is important in this arrangement to ensure that the two parts of the reiiector are accurately located in their operative positions, and one convenient arrangement to this end (shown in Figures S-lZ) comprises a main supporting apertured plate J formed with a true plane surface and mounted so that such surface lies accurately at right angles to the axis, and two frames Kil carried by the supporting plate .l respectively for carrying the two parts LL1 of the redector. Each of these frames K Kl is spring-pressed into engagement with the plane surface on the plate J and has an opening provided with a shoulder K2 or Ka accurately parallel to the plane of engagement of the frame with the plate I, the reflector part L or L1 being iitted into such opening in close engagement with the shoulder K2 or K2. The openings in the two frames KK1 register laterally with one another so that, in the operative position, the two reliector parts LL1 are close together and present an almost continuous reflecting surface accurately located in the correct position.

The two frames KKl are pivoted together at one end, for example by means of a ring J1 engaging in arcuate recesses K415i cut in the outer surfaces of the frames KKl at their contiguous edges, such ring J1 being attached to a pivot pin 52 which passes between the edges of the frames and through a bearing hole in the supporting plate .l to a head J3 which is spring-pressed away from the plate I, such spring I4 constituting one of two springs for urging the frames KK1 into engagement with the plane surface of the plate I. The second spring M is at the other end of the frames and likewise surrounds a pin M1 passing through a bearing hole in the plate I. A head M2 on this second pin M1 has projections M3 engaging between the contiguous edges KSK of the frames Y KKl so that when the head M2 is rotated it will force the two frames apart. The two frames KKl have lugs KSK9 carrying the ends of a tension spring K10 for pulling the two frames towards one another into engagement with the pin Ml and the projections M3 on its head M2.

Thus, in the operative position, the two frames KKl are pulled together into engagement with the pin M1 and in this position the edges of the two reliector parts LL1 lie close together and surround the blade A with only slight clearance. When the blade A is to be loaded into position or removed therefrom, the head M2 on the second pin M1 is rotated to force the frames KKI apart suliciently to enable the blade A to be inserted or withdrawn axially without touching the edges of the reector parts LLl. A relatively small separating movement of the frames will usually suiiice, provided that the blade A in its loading movement is appropriately guided by a generally helical guide slot B1 in the manner above-mentioned to suit its twist. In practice, it is desirable to provide an interlock to prevent movement of the blade until the reliector parts LLl have been separated. For example, such separation may operate an electric switch for energising a solenoid controlling a detent engaging with the blade holder.

The slight break in the continuity of the reflector LL1 at the edges of its parts will not in practice interfere very seriously with the proper projection of the image of the complete blade section profile. Such brealf` can 'oe arranged to be adjacent to any desired portion of the blade section and need not be adjacent to the leading and trailing edges of the blade.

It will usually be desirable, as mentioned above, for the apparatus to be readily adjustable for dealing with different sizes and shapes of blade. If the number of sizes and shapes to be dealt with is small, the simplest arrangement is to malte the complete reector assembly detachable from the ixed base, and to provide a set of interchangeable assemblies, one or each different size or shape of blade.

More generally, it is preferable to make the individual reiiectors or reflector parts detachable from their mountings, a set of interchangeable reectors being provided as required, and to provide for axial adjustment of the mountings as indicated in Figure l to suit different spacings between the section prole planes.

Figures 13-15 show another reector construction, employing full reection, wherein the reflector is constituted by a number of reflecting elements N having generally sector-shaped inner ends, radiating from the optical axis of the projection system F and angularly spaced apart from one another. Each element N slides in a radial groove in an annular boss O1 on the reflector mounting O and is held therein by a cover plate O2 secured to the boss O1. At its outer end, each element N carries a pin N1 which is pressed outwardly by a spring N2 abutting against the outer surface of the boss O1. A cam plate P, attached to a rotatable ring P1 housed in an outer recess in the mounting O, has a number of inwardly directed cam projections P2 each coopexating with the outer end of one of the reiiector elements N, the springs N2 serving to keep the elements N in engagement with the cam projections P2. An annular retaining cover Q attached to the outer portion of the mounting O serves to keep the rotatable ring P1 in place. rihis Vcover Q also has a recess Q1 in its'inner edge, in which engages a projection P3 on the rotatable ring P1, so that the ends of the recess Q1 afford stops to limit the rotation of the ring P1.

With this arrangement, the sector-shaped inner ends of the elements N, in their operative position, are pressed inwardly by the cam projections P2 so as to lie close to the surface of the blade A. The sectors are angular-ly lspaced apart so as to occupy approximately 50 per cent of the area (assuming there is only one reilector), so that the intensity of the light beam reilected by the elements N from the section prolile A3 is approximately equal to the intensity ot the light beam transmitted through the gaps between the sectors from the section profile A2. The projection system F is thus divided into radial zones appropriate to the individual section proles. The back of each element N is chamfered off at its edges, as shown in Figure l5, so as to interfere to a minimum extent with the rays from the section A2. When the blade A is to be loaded into position or Withdrawn therefrom, the rotatable ring P1 is rotated, so that its projection P3 comes to the other end of the slot Q1. This rotates the cam plate P, so that the elements N are moved outwardly by their springs N2 to provide adequate clearance for movement of the blade A.

lt will be appreciated that the foregoing arrangements may be modilied in various ways within the scope of the invention and may be employed for the examination of section profiles of bodies other than turbine blades.

What we claim as our invention and desire to secure by Letters Patent is:

l. An optical system for simultaneously projecting on to a single image plane images of the profiles of a plurality of plane sections of a body in planes parallel to but at different distances from such image plane, comprising reecting means for superirnposing images of individual section proiiles in a single object plane, such reecting means consisting of at least one plane partial reector divided into parts lying in a single plane and spaced around the body under examination, said reilector plane being parallel to said image plane, a single objective having its optical axis perpendicular to the said planes for projecting an image from such object plane on to the image plane, mounting means whereby the reflector parts can be moved towards or away from each other in a plane at right angles to the optical axis of the objective, and means for adjusting the reiiecting means in the direction of the optical axis, the mounting means comprising at least one guide surface deiining a plane lying accurately at right angles to the optical axis and guiding means whereby the reector parts can be caused to slide over such guide surface while maintaining exact parallelism therewith.

2. An optical system as claimed in claim Lin which the said guiding means comprises movable frames which can slide over the guide surface, spring means urging the `frames into engagement with the guide surface, and means for mounting the retiector parts respectively' in the movable frames with their reflecting surfaces accurately parallel to the guide surface.

3. An optical system as claimed in claim l, in ywhich 8 the said plane reflector is totally reflecting and is divided into a number of angularly spaced elements each approximately of sector shape, whereby the reilector acts as partial screening means for segregating sector-shaped zones of the objective for association with individual section profiles. Y'

4. An optical system as claimed in claim 3, in which the said mounting means -for the reiiector parts comprises approximately radial guides along which the elements can slide, a rotatable ring, and cams carried by such ring for controlling the movements of the elements in their guides.

5. An opical system as claimed in claim l, in which the said plane partial reector is partially transparent over its whole iield and its parts in their operative posi` tions fit closely together and form a central opening which completely surrounds the periphery of the body under examination and conforms closely to the peripheral #bape thereof. t

An optical system as claimed in claim 5, in which the said guiding means comprises movable frames which can slide over the guide surface, and means for detachably mounting the reilector parts respectively in the movsible frames.

7. An optical system for simultaneously projecting on to a single image plane images of the profiles of a plurality of plane sections of a body in planes parallel to but at different distances from such image plane, comprising a single objective having its optical axis perpendicular to the said image plane for projecting an image on to the image plane from an object plane coincident with the plane of the section prole furthest from the objective, a plane partial reflector associated with each other section prole for bringing a reflected image of the associated prole into such object plane, the number of plane partial re'llectors thus being one less than the number of section profiles, each such reflector being divided into parts around the body under examination, and mountmeans whereby such parts can bemoved towards or away from each other in a plane at right angles to the optical axis of the objective, such mounting means including movable frames constrained to move in a plane at right angles to the optical axis and means whereby the reilector parts are detachably mounted respectively in the movable frames.

S. An optical system as claimed in claim 7, in which each plane partialrreector is partially transparent over its whole iield and has transmittance such that the intensity of the beam of light passing through the objective from any one section proiile is approximately the same as that from any other section profile.

9. An optical system as claimed in claim 7, including means for independently adjusting each plane partial reiiector in the direction of the optical axis of the objective to suit dilerent spacings between the planes of the section profiles.

lO. An optical system for simultaneously projecting on to a single image plane images of the profiles of a plurality of plane sections of a body in planes parallel to but at different distances from such image plane, comprising a single objective having Yits optical axis perpendicular to the said image plane for projecting an image on to the image plane from an object plane, and reiecting means for superimposing images of individual section profiles in such object plane, such reflecting means comprising at least one totally reflecting plane reector divided into a number of angularly spaced elements each approximately of sector shape, whereby the reflecting means acts as partial screening means for segregating sector-shaped zones ofV the objective for association with individuai section proles.

l l. An optical system as claimed in claim l0, including mounting means 'for the retiector elements whereby such elements can be moved in a plane at right angles to the 9 optical axis of the objective towards or away from such References Cited in the le of this patent axis UNIT TE P EN 12. An optical system as claimed in claim l0, including ED STA S AT TS 2,607,267 Fultz Aug. 19, 1952 2,629,936 Cronstedt Mar. 3, 1953 

